This invention relates to ferroelectric, or tilted chiral smectic, liquid crystal display devices which have enhanced alignment.
In order to obtain the desired driving characteristics for optical modulating elements incorporating a bistable liquid crystal, it is necessary that the liquid crystal interposed between a pair of parallel substrates have a molecular alignment such that the two stable states are reversibly changed effectively irrespective of the state of application of the electric field. Various methods have been suggested for obtaining such molecular orientation. U.S. Pat. No. 4,561,726 (Goodby et al.) discloses alignment of ferroelectric liquid crystal display devices through the use of specific ordering substances such as polyimides, polyamides and polyesters that satisfy two criteria. They should be capable in the bulk form of being elongated at least 50 percent before fracturing and after an elongation of at least 50 percent, they should retain a length at least 20 percent more than the original length before elongation.
U.S. Pat. No. 4,367,924 (Clark et al.) discloses an-electro-optical device including a chiral smectic C or H liquid crystal disposed between flat plates treated, e.g., with poly(n-methyl-3-aminopropyl-trimethoxysilane), to enforce molecular orientation parallel to the plates. The plates are spaced by a distance sufficiently small to ensure unwinding of the helix typical in a bulk of the smectic C or H material to form two stable states of the orientation field.
U.S. Pat. No. 4,563,059 (Clark et al.) discloses a liquid crystal device including a ferroelectric liquid crystal disposed between plates treated, e.g., by rubbing or oblique SiO evaporation, to enforce a particular ferroelectric molecular orientation to the plates. The devices employ, alone or in combination, non-planar boundary condition, polar boundary conditions, boundaries with multiple physical states, intrinsic spontaneous splay distortion of the polarization orientation field, combined ferroelectric and dielectric torques, and layer tilted with respect to the plates.
U.S. Pat. No. 5,109,293 (Matsunaga et al.) discloses a ferroelectric liquid crystal display element in which oblique alignment layers of SiO are inclined with respect to a substrate surface and have opposite inclination directions which are formed on opposing surfaces of a pair of substrates having transparent electrodes. A ferroelectric liquid crystal is injected into the space between the substrates only in a direction opposite to the inclination direction of the oblique alignment layers.
European Pat. Pub. No. 0 450 549 Al (Canon) discloses a ferroelectric liquid crystal device and apparatus having a pair of substrates with orientation control films of a fluorine-containing aliphatic polyimide or a fluorine-containing alicyclic polyimide. The fluorine-containing aliphatic polyimide or alicyclic polyimide has a structural unit expressed by the following general formula: ##STR1## wherein R.sub.1 is a tetravalent organic residue and R.sub.2 is a divalent organic residue, at least one of R.sub.1 and R.sub.2 being a alicyclic or aliphatic organic residue containing fluorine and n is 0 or 1.
Marshal, Kenneth L., "Laser Damage Resistant Polysiloxane Polymers as Homeotropic Alignment Layers for Liquid Crystal Devices," Mol. Cryst. Liq. Cryst. Letters, Vol. (5), pp. 133-138, discloses a class of commercially available polysiloxane resins, i.e., "glass resins," which can be used to produce homeotropic aligning layers of high optical quality and laser damage resistance for liquid crystal devices with cyanobiphenyls, i.e., nematic liquid crystals, at cell spacings as large as 167 microns.